Mechanical strength variability of deformed reinforcing steel bars for concrete structures in Ethiopia

www.nature.com/scientificreports OPEN Mechanical strength variability of deformed reinforcing steel bars for concrete structures in Ethiopia Tariku Achamyeleh1,2*, Hüseyin Çamur1, Mahmut A. Savaş1 & Ali Evcil1 The paper presents statistical analysis of mechanical strength and linear density properties of deformed reinforcing Grade 60 steel bars. Two different lots of samples are identified based on test years for the years 2015–2017 as Lot 1 and 2018–2020 as Lot 2. Yield strength (YS), tensile strength (TS), elongation, mass per length and characteristic ratio of TS and YS are analyzed for rebar diameters of 8, 10, 12 and 16 mm considering both lots. Mechanical and linear density properties are compared statistically using range, mean, standard deviation, coefficient of variance, skewness and kurtosis of the recorded sets of values. Moreover, the results of YS, TS and elongation are analyzed separately by one-way analysis of variance for both lots. The result shows that the aggregate mean values of YS, TS and elongation for Lot 1 and Lot 2 are 593.1 MPa, 701.1 MPa, 14.78%; and 572.5 MPa, 673.8 MPa, 15.47%, respectively. Even though there is a slight decrement in values of YS and TS and increment in elongation from Lot 1 to Lot 2, both lots exceeded values recommended by ASTM A615 standard. Furthermore, with 95% confidence interval, one-way analysis of variance showed that the aggregate data of rebars are dissimilar in terms of YS, TS and percentage elongation with figures showing decrement from Lot 1 to Lot 2. Concrete is resilient for compressive strength but weaker to tensile loads. Moreover, resistance of reinforced concrete structures for cyclic loading solely depends on the reinforcing steel bars which are considerably more demanding than its basic function. The energy absorption and dissipation during inelastic deformation depends almost entirely on the ductility of the reinforcing steel. Investigating the mechanical strength of reinforced steel bar determines the overall strength of concrete structure. Reinforcing steel bars play a key role as a construction material. The properties of reinforcing steel bars must be known for the users before being applied for design or construction purposes because they are mainly used in construction projects that pose danger to human life such as building, bridges and furniture industries if improperly designed1. Steel shows a wide range of mechanical and physical properties of which the mechanical strength factor is the dominant property2. The quality characteristics of reinforcing bars in steel structural engineering is commonly studied in terms of its mechanical properties such as, yield strength (YS), tensile strength (TS) and e longation3. These characteristics of steel are illustrated in generic stress–strain c urve1,4. Thus, any improvement in strength characteristics of steel will promote the reliability and durability of the building structure in which it is used2. Investigating mechanical properties of deformed reinforcement steel bars have become area of interest by many scholars particularly number of statistical studies conducted explicitly with the variability of the mechanical properties of reinforcing steel b ars2–18. Effect of linear density properties and chemical composition variability 19,20 studies were also investigated . In these studies, variability of yield strength, tensile strengths, elongation at fracture, mass per length and ratio of tensile strength to yield strength were examined and compared with A CI21, IS22 and ASTM s tandard23–25. This variability is thought to be caused by dissimilarity in the manufacturing practices and quality control procedures followed by different firms, as well as possible variations in geometric size of the bars, steel strength, and rate of loading6. According to Mirza and M acGregor5, test results of about 4000 ribbed reinforcing steel bars were studied to statistically determine relationships for various mechanical strengths. The study covered wide range of bars designated from No. 3 to No. 18. The sample included reinforcement steel bars of grade 40 and 60. The mean and coefficient of variation of the two grades were analyzed for yield strength and tensile strength. 1 Department of Mechanical Engineering, School of Applied Sciences, Near East University, 99138 Nicosia, KKTC, Turkey. 2Department of Mechanical Engineering, Faculty of Technology, Debre Tabor University, Debre Tabor, Ethiopia. *email: Scientific Reports | (2022) 12:2600 | https://doi.org/10.1038/s41598-022-06654-1 1 Vol.:(0123456789) www.nature.com/scientificreports/ Diameter of bar (mm) Test sets 8 10 12 16 Total samples Lot 1 37 44 40 31 152 Lot 2 39 27 60 51 177 Table 1.  Samples by lot and diameter. Djavanroodi and Salman6 analyzed statistical variability of mechanical properties and weight of grade 60 reinforcing steel bars. The study investigated 130 samples for yield strength, tensile strength and elongation. 60 bars were investigated for variability of weight. Carrillo et al.4 characterized stress–strain curves of steel reinforcing bars marketed in Bogota. 60 samples with diameters ranging from 9.5 mm to 25.5 mm were tested for tensile strength. The aggregate results were statistically analyzed and compared with other countries i.e. US, India and Mexico. Tavio et al.8 in addition to yield strength, tensile strength and elongation, investigated ratio of tensile to yield strength of various steel grades and bar sizes. The test results were analyzed and compared among steel grades and with ASTM, IS22, ACI21 and Russian standards. Rafi et al.13 investigated the variability of chemical and mechanical properties of cold-twisted and hot-rolled ribbed reinforcement steel bars of diameters ranging from 10 to 40 mm. The result showed a large variation in reinforcement bar strength for which design implications were studied as failure mode of flexure members might exhibit a change from ductile to brittle. Bournonville et al.26 investigated statstical variability of mechanical properties of of reinforcement steel bars produced in the US and Canada. 100 samples were collected from 29 reinforcemnt steel manufacturing industries. The statistical report included parameters such as mean, median, standard deviation, cofficient of variance, skewness and kurtosis. Alo et al.27 reported statistical assessment of mechanical properties of locally produced and imported reinforced steels used in Nigeria. One-way ANOVA analysis was conducted to indicate the variability of the reinforcing bars in terms of yield strength, tensile strength and elongation. Variability analysis of mechanical properties of reinforcement steel bars plays a great role in assessing homogeneity of steel products used in the construction projects. Hence, the purpose of this work is to statistically analyze mechanical and linear density properties of reinforcing bars that were used in Ethiopian construction industr (...truncated)